Various methods are available for excavating and conveying earth. In particular, a method using a wheeled vehicle machine and a method using a tracked vehicle machine are available for conveying earth while continuing an excavation operation on an irregular or soft ground. The wheeled vehicle machine is suitable for long range conveyance over a relatively hard ground, while the tracked vehicle machine is suitable for short range conveyance over an irregular or soft ground.
Earth excavating and conveying methods using a tracked vehicle machine are described below:
A first method for excavating, scraping and conveying earth involves a blade 101 provided at the front part of a bulldozer 100, shown in FIG. 15.
A second method for earth movement involves a scrape dozer 110, shown in FIG. 16. While moving forwardly, the scrape dozer 110 lowers a bowl 111, which is provided at its front part. Simultaneously, an apron 112 is opened, and excavated earth is loaded into the bowl 111 while additional earth is excavated by a cutting edge 113. When loading of the bowl 111 is finished, the bowl 111 is lifted upwardly, the apron 112 is closed, and the scrape dozer 110 conveys the excavated earth to a specified location. For scattering earth from the bowl 111, the apron 112 is opened and earth is pushed out of the bowl 111 by an ejector 114.
A third method for earth movement involves towing a trailing wheeled scraper 120, shown in FIG. 17. The trailing wheeled scraper 120 lowers the bowl 121 while advancing. Simultaneously, the wheeled scraper 120 opens the apron 122 and loads earth into the bowl 121 while continuing the excavating operation. When the loading of the bowl 121 is finished, the bowl 121 is lifted upwardly, the apron 122 is closed, and the excavated earth is conveyed by the wheeled scraper 120 to a specified location. For scattering earth from the bowl 121, the apron 122 is opened and earth is pushed out of the bowl 121 by the ejector 123.
A fourth method uses a bucket dozer 130, shown in FIG. 18, as proposed in Japanese Utility Model Application Laid-open No. (Y2) 1-31632. A bucket 133, which is pivoted about a pin 132, is provided at the front part of the tractor 131 and, in excavation and loading, excavated earth is loaded into the bucket 133 while additional earth is excavated by the cutting edge 134. For conveying the excavated earth, the bucket 133 is lifted upwardly by the lifting cylinder 135 and the bucket dozer 130 then conveys the excavated earth to the specified location. For scattering earth from the bucket 133, the bucket 133 is pivoted about pins 132 by the bucket cylinder 136, as shown with a two dot broken line in FIG. 18.
However, the methods using the above-described types of equipment include the problems as described below.
In the first method using the bulldozer 100, a large frictional resistance is caused since excavated earth is conveyed by pushing earth collected in front of the blade 101. In addition, the vehicle speed is slow, and earth drops out from both sides of the blade 101. Therefore, the earth excavating and conveying work is inadequate.
In the second method using the scrape dozer 110, the bowl 111 into which excavated earth is loaded is located in front of the center of the vehicle machine. Therefore, the center of gravity is excessively shifted to the front part of the vehicle machine when the bowl is filled with earth, and a uniform distribution of ground contact pressure by the track shoes cannot be maintained. Accordingly, the track shoes of the scrape dozer 110 are liable to slip, a large tractive force cannot be obtained, and the vehicle machine refrains from entering into a soft ground. In addition, the amount of earth conveyed per unit of vehicle weight is small.
In the third method using the trailing wheeled scraper 120, the vehicle machine cannot be operated on a soft ground because of the wheels. In addition, the trailing wheel scraper 120 cannot be retracted. Therefore, the working conditions are limited, and the work is inefficient.
In the fourth method using the bucket dozer 130, the bowl 133 for loading earth is provided only at the front part of the vehicle. Therefore, during the conveyance of loaded earth the center of gravity is shifted to the front part of the vehicle, the vehicle is unbalanced, and the distribution of ground contact pressure is not uniform. Accordingly, the track shoes of the bucket dozer 130 are liable to slip. It is also difficult for the bucket dozer to work on a soft ground. The amount of earth conveyed per unit of vehicle weight is small. In addition, it is difficult to adjust the rate at which earth is to be ejected during an operation of scattering earth.